What is the target air content for concrete with a maximum aggregate size of 3/4 inch in bridge decks according to ACI?

The target air content for concrete with a maximum aggregate size of 3/4 inch in bridge decks is specified to be around 5%. This level of air content is crucial for ensuring the durability of concrete in bridge decks, particularly in environments where freeze-thaw cycles and de-icing chemicals are a concern.

Air entrainment helps to create small, uniform air bubbles within the concrete mix. These bubbles act as stress relievers when water expands upon freezing, thereby reducing the potential for cracking and damage to the concrete structure. The prescribed 5% air content balances the need for workability and durability, ensuring that the concrete can withstand the stresses it will encounter throughout its service life while maintaining proper flow and placement characteristics.

In contrast, options that suggest lower air contents like 3% or higher values such as 7% and 10% do not align with the established standards for concrete in bridge deck applications. Lower air content may not provide adequate protection against freeze-thaw damage, while excessively high air content could compromise the concrete’s strength and load-bearing capacity. Achieving an optimal air content of around 5% is thus essential for the performance and longevity of bridge decks.